OSMEC. Computer mechanism design: basic examples.
Abstract:ESDU 98023 gives worked examples to provide insight into the basic analysis and design of planar linkage mechanisms using OSMEC. Example 1 describes in detail how OSMEC is used to derive the motion, forces and drive torque in a four-bar linkage to move the louver of an air-conditioning system through a 90 degree arc. The link lengths and the crank angular displacement are varied. Graphs of the drive torque required from the motor and the bearing forces throughout the linkage are plotted and the significance of a transmission angle is discussed. The procedure for designing the mechanism is described step-by-step by identifying and discussing each software command issued to the OSMEC software. Example 2 shows how one of three trunnion-mounted rams is selected on the basis of the results of an analysis of a mechanism used to move boxes of breakfast cereal. The thrust required from the ram in each mechanism is analysed and the maximum values of bearing pressure and contact surface velocity are determined. Example 3 considers the design of an alternative mechanism to meet the requirements of Example 2 and demonstrates the development of a pivoted-slider mechanism driving a slider entity from an offset point on the sliding link. Example 4 deals with a ten-bar linkage used to drive a needle-bar mechanism. The mechanism drive torque during the start-up phase is compared with that under steady running conditions. Example 5 shows how a coupler curve can be plotted for an example of Stephenson's six-bar linkage that incorporates an approximate dwell for a segment of the crank rotation. An assessment is made of the sensitivity of the mechanism performance to small deviations from the nominal link dimensions.
|Data Item ESDU 98023|